This invention relates to bindings for books, notebooks and other configurations of stacks of paper or other sheet material and, more particularly, to a metallic ring binder formed of a continuous wire. A binding formed of a continuous segment of metallic wire is commonly used in the binding of stacks of sheet material such as paper to form books, particularly notebooks. One form of binding is constructed by bending the wire in the shape of a spiral, and then passing turns of the spiral through free formed apertures in the sheet material. Such a binding is known as a spiral binding and has been in use for many years. A characteristic of the spiral binding is the employment of a single aperture for each turn of the spiral, with the apertures being spaced apart between centers by a distance equal to the spacing between turns of the spiral. The apertures are made sufficiently small to allow for an adequate amount of sheet material therebetween to inhibit tearing of the sheet material by the wire.
The spiral binding has been found to provide adequate strength for holding together the sheet material, particularly paper bound into notebooks. However, the spiral binding suffers a disadvantage in that a cumbersome process is required for assembly of the binding, the processing requiring the rotation of the spiral for threading the end of the spiral into successive ones of the apertures.
The foregoing disadvantage is avoided in a ring formed of wire binding wherein the wire is bent back and forth to provide a succession of tabs or fingers extending from a set of colinear sections of wire. The set of colinear sections of wire may be referred to as the backbone of the binding. Prior to insertion of the wire into the apertures of the sheet material, the bent wire has the configuration of a comb, rather than a spiral. Each finger is composed of two sections of wire bent back upon each other. The fingers of the comb are then curved to pass through the apertures and form rings which terminate on the backbone. The rings hold the sheet material together.
The ring binding is used as a substitute for the spiral binding. Machinery exists for the simultaneous bending of all of the fingers for simultaneous formation and insertion of the rings into all of the apertures of the sheet material. By way of example in the construction of such a ring binding, U.S. Pat. No. 4,373,558 in the name of K. H. Dawson (at FIG. 1) shows the comb-like form of the bent wire and a machine for bending the wire. In the construction of the ring binding, it has long been the practice to conform the shape of the binding as closely as practicable to the shape of the spiral binding. Thereby the two bindings may be used interchangeably without loss of strength and utility.
The conforming of the shape of the ring binding to the shape of the spiral binding has been accomplished by making each finger as narrow as practicable whereby the double turns of wire in each turn of the binding approximate the single pass of wire in a turn of the spiral. The spacing between turns of the ring binding approximates the spacing between turns of the spiral binding. This spacing is substantially larger than the width of the finger of the ring binding. In the ring binding, the apertures are somewhat larger than those of the spiral binding to accommodate the double wire of each turn of the ring binding.
Yet another form of binding is constructed of plastic sheet stamped in the shape of a comb wherein the width of the fingers is approximately equal to the spacings between edges of the fingers. The comb is set with a permanent curvature to provide a set of rings which pass through elongated rectangular apertures in the sheet material which is to be bound. This plastic binding is widely used today, primarily because of the facile manner in which it can be inserted in the apertures. Such insertion is accomplished with the aid of machinery which spreads the rings apart for threading the fingers into the apertures, and thereafter the machine allows the rings to close to complete the binding. A problem arises in that the plastic binding lacks much of the strength present in the metallic wire binding. This is particularly true in the event that the plastic ages, in which case the plastic may crack. While the aforementioned metallic ring binding may be employed to provide the additional strength, the ring spacing and width does not fit the elongated rectangular apertures of the plastic ring bindings. This is a significant inconvenience since the perforation equipment for producing the elongated apertures is widely used and readily available.